1. Field of the Invention
The present invention relates to a gas valve assembly, and more particularly, to a permeable gas valve assembly that controls fluid flow from a downstream fluid source to an upstream processing tool.
2. Description of the Related Art
Many industrial processing and manufacturing applications require the use of highly toxic fluids. The manufacture of semiconductor materials represents one such application wherein the safe storage and handling of highly toxic hydridic or halidic gases becomes necessary. Examples of such gases include silane, germane, ammonia, phosphine, arsine, stibine, hydrogen sulfide, hydrogen selenide, hydrogen telluride, and other halide compounds. As a result of toxicity and safety considerations, these gases must be carefully stored and handled in the industrial process facility. The semiconductor industry in particular relies on the gaseous hydrides of arsine (AsH3) and phosphine (PH3) as sources of arsenic (As) and phosphorus (P) in ion implantation. Ion implantation systems typically use dilute mixtures of AsH3 and PH3 at pressures as high as 1500 psig. Due to their extreme toxicity and high vapor pressure, their use, transportation and storage raise significant safety concerns for the semiconductor industry.
For example, arsine is an extremely toxic gas that is used by the semiconductor industry and typically stored in pressurized containers at about 250 psi. The handling of arsine cylinders in production environments presents a wide variety of hazardous situations. A leak in one 140 gram cylinder of arsine could contaminate the entire volume of a 30,000 square foot building with 10 foot high ceilings to the Immediate Danger to Life and Health (IDLH) level. If the leak was large, the contamination could occur in a few minutes, which would mean that for many hours there would be extremely deadly concentrations in the area near the source of the spill.
Gas pressure regulating valves of the type for delivering gas at a relatively low pressure, have been known and used for many years. However, these valves are subject to leakages of the highly pressurized gas along valve stems. Unless some provision is made for preventing such leakage, the build-up of high pressure gas leakage in trapped volumes within the valve device can introduce an unintended bias into the regulator and produced distortion of the delivery control. In order to nullify the effect of leakage, some pressure regulating valves resort to the use of a constantly open atmospheric vent port for releasing gas leakage directly to the atmosphere. Clearly, in the case of inflammatory gas or explosive gases the possible accumulation of released gas in a confined area becomes a serious health and safety hazard, and an open port is not an option.
In view of the serious potential for injury or death that could result from an unintended release of these fluids, the prior art discloses systems for preventing such catastrophic release of toxic fluids. U.S. Pat. Nos. 5,704,965; 5,704,967; 5,707,424; and 5,518,528 teach systems for storage and dispensing of hydridic and halidic gases which operate at ambient temperature by using a pressure reduction to desorb toxic fluids from zeolite materials having high storage (sorptive) capacity for these gases. However, the purity of the gas is reduced due to residual absorbant material that may be entrained within the discharging gas.
Accordingly, there is a need in the art for a gas assembly delivery system that avoids the disadvantages of known delivery systems including the avoidance of releasing highly pressurized toxic gases directly to the atmosphere or reducing the purity of the discharged fluid due to entrained absorbent material.
It is a broad object of this invention to reduce the possibility of accidental spillage or release of toxic liquid or gases.
Another object of this invention is to eliminate the need for sorbents to control the handling, storage and delivery of toxic fluids.
A further object of this invention is to provide a discharge system that constrains the flow of gas during normal operation as well as during any kind of valve mishandling or valve failure.